Audio peripheral device having controller for power management

ABSTRACT

A controller for a powered loudspeaker for use in a computer system including a bus monitor configured to monitor a bus for predetermined activity and a power management control unit coupled to the bus monitor. The controller is configured to turn off power supplied to the powered loudspeaker responsive to an absence of predetermined activity on said bus. After a predetermined interval, or upon detection of restoration of activity, the power is turned back on.

FIELD OF THE INVENTION

The present invention relates to speakers for personal computers andparticularly to a power control mechanism for a Universal SerialBus-based PC speaker controller.

DESCRIPTION OF THE RELATED ART

The Universal Serial Bus (USB) specification is a proposed standardrecently promulgated by a group of computer companies including CompaqComputer Corporation, Digital Equipment Corporation, IBM, IntelCorporation, Microsoft Corporation and Northern Telecom. Described beloware various aspects of the Universal Serial Bus. Further backgroundconcerning the Universal Serial Bus may be obtained from the UniversalSerial Bus Specification, Revision 1.0, which is hereby incorporated byreference. The Universal Serial Bus is intended as a bi-directional,isochronous, low-cost, dynamically attachable, serial interface topromote easy PC peripheral expansion and provide full support forreal-time voice, audio, and compressed video data. The Universal SerialBus provides two-wire point-to-point signaling in which the signals aredifferentially driven at a bit rate of 12 megabits per second. TheUniversal Serial Bus includes support for both isochronous andasynchronous messaging at the 12 megabit per second data speed.

The Universal Serial Bus specification defines a Universal Serial Bussystem in terms of Universal Serial Bus "interconnects", "devices", and"hosts". A Universal Serial Bus interconnect defines the manner in whichdevices are connected to and communicate with the host, including bustopology, data flow models, scheduling, and interlayer relationships. Inany given Universal Serial Bus topology, there is only one host.

Universal Serial Bus devices include hubs and functions. Hubs provideadditional attachment points to the Universal Serial Bus and may beintegrated with a host, which ordinarily provides only one attachmentpoint for connecting a hub or a function. Functions provide capabilitiesto the system, such as joystick, keyboard, microphone, and speakercapabilities.

The basic data transfer protocol of the Universal Serial Bus isdescribed as follows, with particular attention to FIG. 1. FIG. 1 is adiagram of the basic packet transfer 1000 of the Universal Serial Bus.The basic transfer 1000 includes a token packet 1002, a data packet1004, and a handshake packet 1006. Each packet is preceded by asynchronization field SYNC which is used by input circuitry to alignincoming data with the local clock. It is defined to be 8 bits in lengthand is stripped out by the connector interface.

Following the SYNC field in each packet is a packet identifier (PID(T)for the token packet, PID(D) for the data packet, PID(H) for thehandshake packet, and PID(S) for the start-of-frame packet, which may beconsidered a type of token packet). The packet identifiers PID(T),PID(D), PID(H) and PID(S) include a 4-bit identification field and a4-bit check field used to identify the format of the packet and type.There are two types of token 1002 packet ID fields PID(T). These denote(i) a data transfer from the function to the host; and (ii) a datatransfer from the host to the function. In addition to the packet ID,PID(T), the token packet includes an 8-bit address field ADDR and a3-bit end point field, ENDP. The address field ADDR of the token packetspecifies the function that it is to receive or send the data packet.The end-point field ENDP permits addressing of more than one subchannelof an individual function.

Only one type of start-of-frame packet identification field 1008,PID(S), is defined: a start of frame time stamp. The address andendpoint fields of the token packet are replaced in the start of framepacket with a time-stamp field. The time-stamp field for the start offrame packet provides a clock tick which is available to all devices onthe bus. The start-of-frame packet is sent by the host every 1 ms±0.01%.In addition, for both the token and start-of-frame packets, a 5-bitcyclical redundancy checksum (CRC) field is provided.

The data packet 1004 includes a packet identifier PID(D), a data fieldDATA, and a 16-bit cyclical redundancy checksum field, CRC16. Two typesof packet IDs for the data field, data 0 and data 1. identify whetherthe data packet is being sent for the first time or whether being sentas a retry. The data field DATA may vary in length from 0 to N bytes.Failure of the cyclical redundancy checksum on the data field DATAcauses the receiver to issue an error ERR handshake.

The handshake packet 1006 includes only a packet identifier PID(H), ofwhich there are four types. An acknowledge handshake, ACK, indicatesthat the receiver will accept the data and that the CRC has succeeded. Anegative acknowledge, NACK, indicates that the receiver cannot acceptthe data or that the source cannot send the data. An ERR field indicatesthat the receiver will accept the data, but that the CRC has failed. Astall handshake packet, STALL, indicates that the transmission orreception pipe is stalled. A stall handshake is defined only forstream-oriented end-points (as distinguished from message-orientedendpoints, discussed below).

Data flow on the Universal Serial Bus is defined in terms of "pipes." Apipe is a connection between a host and an endpoint. The UniversalSerial Bus defines "stream" and "message" pipes. For a stream pipe, datais delivered in prenegotiated packet sizes. Data flows in at one end ofthe stream pipe and out the other end in the same order. Stream modethus includes flow control and employs no defined USB structure. For amessage pipe, however, a request is first sent to the device which isfollowed at some later time by a response from the end-point. Messagepipes thus impose a structure on the data flow, which allows commands tobe communicated. These commands can include band-width allocation.

The Universal Serial Bus supports isochronous, asynchronous, andasynchronous interactive data flow. For isochronous data, access to USBbandwidth is guaranteed. A constant data rate through the pipe isprovided, and in the case of delivery failure due to error, there is noattempt to retry to deliver the data. Asynchronous interactive data flowprovides a guaranteed service rate for the pipe, and the retry of failedtransfer attempts. Asynchronous data flow accommodates access to the USBon a band-width available basis and also permits retry of datatransfers.

Scheduling of the Universal Serial Bus is defined in terms of "slots","frames" and "super frames", as illustrated in FIG. 2, which shows anexemplary USB schedule 1100. Frames 1104a and 1104b begin with a startof frame packet, 1108a and 1108b, respectively. Each frame has aduration of time equal to 1±N ms. Each frame, 1104a, 1104b is subdividedinto one or more slots. 1102a, 1102b, for example. Each slot correspondsto some USB transaction, e.g., 1110a, 1110b, 1110c, 1110d. Each slot islarge enough to contain the worst case transmission time of thetransaction to which it corresponds, and includes the effects ofbit-stuffing, propagation delay through cables and hubs, responsedelays, and clocking differences between the host and the end-point. Asuper frame 1106 consists of a repeatable sequence of individual frames,and is the largest schedulable portion of time permitted.

The Universal Serial Bus provides both periodic service and a periodicservice. For periodic service corresponding to isochronous data, a fixedperiod exists between the delivery of start of frame packets to aspecific end-point. However, a periodic service is characterized by avarying period between delivery of start of frame tokens for a givenend-point. Periodic service is given a higher priority in schedulingthan aperiodic service.

Turning now to FIG. 3, there is illustrated an abstracted block diagramof a Universal Serial Bus device, such as a hub or function. UniversalSerial Bus device 1200 includes a device interface 1202 and a classinterface 1204. Device interface 1202 includes device information andcontrol block 1206, which is required for the USB device to attach tothe USB and is independent of the functionality provided by the device.The device interface further includes serial bus interface engine 1210,which provide for management of the bus interface, including performingacknowledgments and recognizing packets that are addressed to the USBdevice. In addition, the interface engine 1210 provides for strippingthe SYNC field from incoming packets. The class interface 1204 includesclass information and control block 1214 which depends upon thefunctionality of the device (for example, hubs and locators). Classinterface 1204 further includes function engine 1216 which relates tothe functionality implemented by the device. A USB device furtherincludes logical buffers, such as packet buffer 1208 and elasticitybuffer 1212. The packet buffer defines the maximum packet size which theUSB device can receive or send. The elasticity buffer relates to howflexible the scheduled generator may be in allocating band-width for theassociated end-point and determines the maximum amount of data thedevice end-point can handle. The various functional blocks of the USBdevice are not shown connected to one another in FIG. 3 because, asdiscussed in the USB specification, the relationship between thecomponents may be implementation-dependent. In addition, a UniversalSerial Bus device may include storage space, local to the USB device,though addressable by the host; and vendor space, which may be definedby the vendor of the device.

While the Universal Serial Bus is intended to be an industry-widestandard peripheral interface, the Universal Serial Bus Specificationdoes not define the relationship between components in Universal SerialBus devices. There is therefore a need to provide novel architecturesfor Universal Serial Bus devices. More particularly, there is a need todefine a novel architecture for a powered speaker and/or microphonecompatible with the Universal Serial Bus Specification.

In addition, while the USB specification defines signaling whereby a USBdevice or hub controller may wake the network from a low power mode, theUSB specification does not define a mechanism whereby the devices maypower themselves down or awaken in response to the signaling. There istherefore a need to provide a USB compatible speaker and/or microphonehaving power management capabilities.

Moreover, in the case of a USB speaker and/or microphone, random powerfluctuations, either at power-up or during normal operation, can feedthrough the speakers and cause annoying "pops" and "hisses" to betransmitted through the speakers. In the extreme case, these can causedamage to the speaker. Accordingly, there is a need to provide a USBcompatible speaker and/or microphone having click suppression when theUSB is unstable or during power-up and power-down.

SUMMARY OF THE INVENTION

Accordingly, there is provided a novel powered loudspeaker implementedto be compatible with a serial bus standard and, particularly, theUniversal Serial Bus specification. The powered speaker includes aspeaker driven by a power amplifier coupled to a power supply. Both theamplifier and the power supply, in turn, are coupled to a UniversalSerial Bus controller. The controller is configured to provide UniversalSerial Bus functionality and compatibility. In addition, a phase lockedloop (PLL) for recovering a timer clock from the received data stream isprovided. One embodiment of the present system further includes afunction whereby the absence of data on the relevant channel is detectedand the output to the speakers is muted in response thereto. A furthercircuit is provided that controls when the output to the speaker isturned on such that no clicks or pops occur at power-up or when thedevice or bus is not stable. In addition, tone control, including bassand treble filters, volume control, and balance between left and rightoutputs (in a stereo version) are provided. Furthermore, powermanagement functionality is provided. If the USB has been idle for apredetermined period of time, the system can place itself into a lowpower sleep mode, or the loudspeaker can be placed into a sleep mode viasoftware from the host.

A microphone compatible with the Universal Serial Bus specification mayalso be provided, either as a discrete unit or integrated with theloudspeaker. The microphone includes a microphone input driving anamplifier coupled to a power feed and gain control. Both are coupled toaudio data circuitry, which includes an analog-to-digital converter andvarious filters, tone and volume control, and a circuit for providing 3Daudio effects. Both the gain control and the audio data block arecoupled to a Universal Serial Bus controller. The controller isconfigured to provide Universal Serial Bus functionality andcompatibility. In addition, a circuit for integrating the microphonesignal into an isochronous USB signal is provided.

A power control circuit for use with a USB microphone/speaker includes amechanism for monitoring activity on the Universal Serial Bus. If theUSB has been idle for a predetermined period, the control mechanism willpower down the speaker. For example, the circuit may be configured tomonitor activity levels on a particular channel of the USB. If theactivity levels are below a predetermined threshold for a predeterminedperiod, the control circuit will cause the power to the device to shutoff or down. In this power down state, however, the circuit will monitorthe bus for host signals indicating that the speaker is to be powered uponce more. In the case of the microphone, the circuit will also monitorthe audio input and cause the microphone to power up in response toreceiving an input signal. Circuitry is also provided for the microphoneto awaken the rest of the system. Circuitry may also be provided tomonitor the level and duration of the input signal. Thus, the microphonewill not power up unless the input exceeds a predetermined activity andduration threshold. In this way, the microphone will not waken thenetwork to process transient undesired inputs.

As noted above, one problem with controlling power to loudspeakers isthat of voltage transients causing hisses or clicks. Accordingly, thereis provided a mechanism to monitor the DC voltage level and turn off thepower if it goes below a predetermined threshold. The volume is rampedto zero after which power may be turned off. After a predetermined time,allowing the transient to subside, the volume may be ramped back to theoriginal level. In addition to monitoring the DC voltage level, thecircuit will monitor the cyclical redundancy checksum for failure andlook for random noise signals. Either can be a source of clicks orhisses. Once either is detected, the circuit will ramp the volume down;after a predetermined time, volume will be ramped back to the originallevel. In another embodiment, the monitoring circuit will continuemonitoring while the volume is down and, when the error condition is nolonger detected, restore the volume to its original level. In addition,high pass filtering may be provided to reject low frequency noise.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a representation of a data packet transfer along with aUniversal Serial Bus.

FIG. 2 is a representation of a scheduling paradigm for the UniversalSerial Bus.

FIG. 3 is a block diagram of an exemplary Universal Serial Bus device.

FIG. 4 is a block diagram of a computer system with audio functionalityaccording to one aspect of the claimed invention.

FIG. 5 is a block diagram of a computer speaker system according to oneembodiment of the present invention.

FIG. 6 is a block diagram of a USB controller for a powered loudspeakeraccording to one embodiment of the present invention.

FIG. 7 is a more detailed block diagram of a speaker control accordingto one aspect of the present invention.

FIG. 8 is a block diagram of a USB controller for a microphone accordingto one embodiment of the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, and with particular attention to FIG. 4, acomputer system 50 is shown according to one embodiment of the presentinvention. Computer system 50 includes a CPU 52 and a cache memory 55coupled to a CPU bus 56. CPU 52 may be any of a variety ofmicroprocessors, including processors compatible with the x86, PowerPC,and 68000 series instruction sets. CPU bus 56 is coupled to bus bridge58, which provides an interface to expansion bus 60. Also coupled to busbridge 58 is a main memory 54. Bus bridge 58 may include a variety ofsystem support logic including cache and memory controls, as well asproviding host/expansion bridge functionality. In addition, bus bridge58 may include a [h] serial bus host interface 64, also referred to as amultimedia peripheral controller, preferably a Universal Serial Bus hostinterface, which provides connectivity to microphone 66 and speaker 68via a serial bus or Universal Serial Bus 76, also referred to as amultimedia bus. Thus, for example, audio data from microphone 66 istransmitted to USB host 64 via USB 76. From there, it is transferred tomain memory 54, from which it is accessible to audio logic 62. Expansionbus 60 may be any of a variety of types of expansion buses, includingbuses compatible with the industry standard architecture (ISA), theextended industry standard architecture (EISA), the Microchannelarchitecture (MCA) or the Peripheral Component Interface (PCI) busarchitecture. It is to be noted that the architecture shown in FIG. 4 isexemplary only and that other configurations are envisaged. Expansionbus 60 may further couple one or more additional bus bridges 70, to oneor more additional expansion buses 72, to which peripheral device 74 maybe coupled.

Turning now to FIG. 5, a more detailed block diagram of a computer audiosystem 100 is shown. Computer audio system 100 is exemplary of, forexample, the computer system 50 shown in FIG. 4. Computer audio system100 includes a computer system 102, which includes a Universal SerialBus host interface 104. Computer system 102 is coupled via a USB cable106 to powered loudspeaker 108. Powered loudspeaker 108 is coupled tothe USB cable 106 at a USB connector (not shown). The USB signals areinput to USB controller 112, which provides an audio signal along line122 to power amplifier 114, which drives speaker 116. USB controller 112further provides an amplifier control signal along line 118 to amplifier114, and a power supply control signal along line 124 to power supply110. Power supply 110 further provides a control along line 120 toamplifier 114. USB Controller 112 is preferably a single integratedcircuit.

USB controller 112 is shown in greater detail in FIG. 6. A USB connector(not shown) receives USB cable 106 (FIG. 5). The USB connector providesthe USB signal to connector interface 200 and function interface 204.Connector interface 200 provides the physical layer translation betweenthe USB differentially-driven signal levels and internal logic levels.Function interface 204 receives the translated signal from connectorinterface 200 and provides the control functions required of allUniversal Serial Bus functions. Thus, for example, function interface204 acts as the serial bus interface engine and as device and classinformation and control blocks discussed with regard to FIG. 3 above.Function interface 204 serves to receive the USB signal, strip off theSYNC field, and provide the signal to the function engine 203.

More particularly, the data will be received at the 1 ms USB frame ratewith the packet size value based on the audio data sampling rate. TheUniversal Serial Bus signal is provided to channel extractor 206 andisochronous timing extractor 210. The received signal is provided inisochronous mode because the audio signal should be provided inreal-time. Isochronous signal timing on the Universal Serial Bus isimplied by the steady rate at which the data is received. Thus, forexample data will be received periodically in periodic mode along thebus based on the sampling requirements of audio data. Because timing onthe Universal Serial Bus during isochronous mode is implied, the clockmust be extracted from the periodic data. Thus, isochronous timingextractor 210 employs a digital phase locked loop to derive internalaudio clocks. Isochronous timing extractor 210 provides the clock toaudio data block 212, which will be described in greater de-ail below.Isochronous timing extractor 210 is further coupled to channel extractor206.

Channel extractor 206 separates the audio subchannel from the other datasubchannels on the Universal Serial Bus. As discussed above, each devicesubchannel on the Universal Serial Bus corresponds to a particularaddress and endpoint combination. Audio data, for example, correspondsto a particular address and endpoint received. Control data correspondsto another address and endpoint combination. The channel extractor 206monitors the various unique endpoints and separates them out from oneanother. As will be discussed in more detail below, this control datacan include volume, balance and tone information. It should further benoted that this information may be provided on separate channels. Sinceone channel on the bus is reserved for bus control, this leaves acapability of up to a total of six speaker control channels. Channelextractor 206 provides the data from the audio control subchannel orsubchannels to speaker controller 208 and the audio data from the audiosubchannel to audio data block 212.

Audio data block 212 can include a mono or stereo digital-to-analogconverter and filter 214 coupled to an analog audio block 216. Analogaudio block 216 performs analog filtering, and provides tone, balance,volume adjustment and muting. Controls for these functions may beprovided from speaker control 208 or from analog potentiometers directlyaffixed to the speaker itself. In addition, audio data block 212 caninclude a 3D audio block which provides stereo enhancement for amulti-dimensional "feel" to the sound. It is noted that in alternativeembodiments, the audio data block 212 is a digital audio data block.

Speaker control 208 reads the control channel received from channelextractor 206 and provides it to audio data block 212. In particular,the control channel or channels can include volume, balance, and toneinformation, as well as a variety of filtering. The filtered audio datasignal is provided to an output driver 218, and is then provided toamplifier 114 of FIG. 4 and then to speaker 116. It should be noted thatwhile the tone, volume, and balance controls may be provided digitallyvia the Universal Serial Bus and hence software, in alternateembodiments, such controls may be provided via physical hardware such asanalog potentiometers and the like.

Speaker control 208 also monitors the audio channel and detects theabsence of data for entering a sleep mode. If such an absence isdetected, speaker control 208 will power down the speaker. Moregenerally, speaker control 208 monitors whether or not the UniversalSerial Bus is idle. Speaker control 208 may detect, for example, theabsence of audio data or clock data. If the bus is idle, the speakercontrol circuit 208 will turn off the power to the speaker in a gradual,controlled fashion. Power is restored only after the Universal SerialBus becomes active once again. In this way, power may be conserved whenthe speaker is not in use. Further, the speaker control circuit providesa control to the audio data circuitry to mute the audio output until thepower is restored. In this fashion, hisses due to the absence of dataand clicks and noises at power-up can be avoided. More particularly, thesystem may be configured such that the volume may be gradually ramped tozero in response to any of a member of warning conditions. This can alsoinclude turning off the power completely upon ramp-down. These caninclude the detection of an aberrational DC level; a bad CRC; or otherrandom values. Power may be restored through ramping the volume back tothe original level, after a predetermined time, or after the warningcondition no longer exists. Additional functionality may be providedwherein the powered speaker can be placed into a powered-down modethrough a software command from the PC. The powered loudspeaker may bepowered up after a predetermined time, or by command from the host PC.Furthermore, high pass filtering, preferably at about 20 Hz, may beprovided for rejection of low frequency "hiss" and "pop" componentsintroduced due to too low a DC level.

Turning now to FIG. 7. a more detailed block diagram of speaker control208 is shown. Speaker control 208 includes a bus monitor 2000 and aclick suppression or power management unit 2002. Both bus monitor 2000and click suppression or power management unit 2002 are coupled to thepower supply (not shown) and are coupled to receive the USB input signalfrom the channel extractor (not shown). Bus monitor 2000 and clicksuppression unit 2002 are further coupled to one another.

Bus monitor 2000 is configured to monitor the USB input signal. Forexample, it may monitor the audio data signal or the clock signal. Whenthe bus monitor detects that the USB is idle, it will transmit a signalto the power supply, causing the power to shut off. A counter 2004 maybe provided, which will count to a predetermined value upon detection ofthe absence of data on the bus. When the value is reached, if there isstill no data on the bus, the power may be shut off. Prior to sendingthe power off control signal to the power supply, bus monitor 2000 mayalso send a control signal to click suppression unit 2002, causing theclick suppression unit 2002 to ramp the volume down to zero beforeshutting off the power.

Bus monitor 2000 will continue to monitor the USB during the power downmode. If the bus monitor 2000 detects activity on the bus, the monitorwill cause the power supply to restore power. Once power is turned backon, the bus monitor 2000 may send a control signal to the clicksuppression unit to cause it to ramp the volume back up.

In addition to responding to the power-on/power-off modes controlled bythe bus monitor 2000, click suppression unit 2002 will also monitor theaudio input for the presence of error conditions. These can includemonitoring for too low a DC level, monitoring for a failed CRC, andmonitoring for random noise. In addition, high pass filtering may beprovided to reject the low frequency noise components. If any of theseconditions are detected, the click suppression unit will cause thevolume to ramp down to zero. Click suppression unit 2002 may continue tomonitor the input and, when the error condition has cleared, restore thevolume in a gradual ramp, so as to avoid clicks, etc. The clicksuppression unit 2002 may also be coupled to turn off the power if theerror condition persists. Once the error condition has been cleared,click suppression unit may restore power, and cause the volume to rampback to its original level. In a still further embodiment, clicksuppression unit 2002 can include a counter 2006 which will begincounting when an error condition has been detected and volume rampinghas begun. After a preset count, the click suppression unit may beconfigured to ramp the volume back up, rather than monitoring during theramping condition. It is to be noted that while the click suppressionunit 2002 and the bus monitor 2000 are shown as discrete units, they maybe part of an integrated power/volume control unit. Thus, FIG. 7 isexemplary only.

Turning now to FIG. 8, there is shown a block diagram of a UniversalSerial Bus-based microphone 5112. An audio signal is provided from anexternal microphone (not shown) to microphone amplifier 5218 and powerfeed 5220. Power feed 5220 in turn is coupled to receive a controlsignal from control unit 5208. Control unit 5208 is further coupled toamplifier 5218 and audio data unit 5212. Control unit 5208 is configuredto provide power management functions. Thus, control unit 5208 isconfigured to monitor the clock, the audio input and the USB foractivity. Control unit 5208 is configured to turn off power to themicrophone on command from the host, or upon detection of a lack of busor clock activity. It is noted that various of these features may beinitialized as desired by software command. In addition, the microphone5112 may be operative in a low power mode such that the USB link may bepowered down while the control unit 5208 monitors the audio input foractivity. If input activity is detected, the control unit will "wake up"the USB link.

In addition, in a manner similar to that described above for thespeaker, gain control 5208 serves to provide control signals to audioeffects unit 5216. Audio effects unit 5216 provides analog filtering,volume and pan control, among other things. Audio effects unit 5216 isfurther coupled to analog-to-digital converter 5214. It is noted that inalternate embodiments, various components such as the audio effects unitmay be implemented with either analog or digital circuitry.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated. It isintended that the following claims be interpreted to embrace all suchvariations and modifications.

What is claimed is:
 1. A powered speaker or microphone peripheral devicecoupled to a computer system by a bus, the peripheral devicecomprising:a speaker or microphone; and a control unit configured tocontrol power to said speaker or microphone, said control unitcomprising a bus monitor configured to monitor the bus for apredetermined activity and to shut off power supplied to said speaker ormicrophone after said bus monitor has detected an absence of saidpredetermined activity on the bus.
 2. The peripheral device as recitedin claim 1, wherein said bus monitor is further configured to shut offpower to said speaker or microphone when a predetermined period of timehas elapsed with an absence of said predetermined activity on said bus.3. The peripheral device as recited in claim 1, wherein saidpredetermined activity comprises clock data.
 4. The peripheral device asrecited in claim 1, wherein said predetermined activity comprises audiodata.
 5. The peripheral device as recited in claim 1, wherein saidcontrol unit is further configured to shut off power to said speaker ormicrophone in response to a command from the computer received over thebus.
 6. The peripheral device as recited in claim 1, wherein said buscomprises a serial bus.
 7. The peripheral device as recited in claim 1,wherein said bus comprises the Universal Serial Bus.
 8. The peripheraldevice as recited in claim 2, wherein said bus monitor comprises acounter for counting said predetermined period of time.
 9. A poweredspeaker peripheral device, comprising:a powered speaker; a speakercontroller configured to receive signals on a bus coupled to saidperipheral device, wherein said speaker controller is further configuredto monitor said bus and to shut off power to said powered speaker afterdetecting bus activity below a predetermined threshold for apredetermined period of time; and said speaker controller furtherconfigured to ramp down the powered speaker's volume before shutting offpower to said powered speaker.
 10. The peripheral device as recited inclaim 9, wherein said speaker controller is further configured tomonitor said bus for said activity while power is off to said poweredspeaker and to restore power to said powered speaker after detectingsaid activity.
 11. The peripheral device as recited in claim 9, whereinsaid speaker controller is further configured to receive audio data andmonitor said audio data for one or more error conditions, wherein saidspeaker controller is yet further configured to shut off power to saidpowered speaker after detecting said one or more error conditions. 12.The peripheral device as recited in claim 9, wherein said speakercontroller is further configured to shut off power to said poweredspeaker in response to receiving a sleep command on said bus from acomputer coupled to said bus.
 13. The peripheral device as recited inclaim 9, wherein said bus comprises the Universal Serial Bus.
 14. Theperipheral device as recited in claim 10, wherein said speakercontroller is further configured to ramp volume back up to said poweredspeaker after restoring power to said powered speaker.
 15. Theperipheral device as recited in claim 11, wherein said speakercontroller is further configured to ramp down volume to said poweredspeaker before shutting off power to said powered speaker afterdetecting said one or more error conditions.
 16. The peripheral deviceas recited in claim 11, wherein said speaker controller is furtherconfigured to restore power to said powered speaker after said one ormore error condition is cleared.
 17. The peripheral device as recited inclaim 11, wherein said one or more error conditions comprise a low DClevel, a failed cyclic redundancy check (CRC), or random noise.
 18. Theperipheral device as recited in claim 12, wherein said speakercontroller is further configured to restore power to said poweredspeaker in response to receiving a wake command on said bus from acomputer coupled to said bus.
 19. The peripheral device as recited inclaim 12, wherein said speaker controller is further configured torestore power to said powered speaker after a predetermined time. 20.The peripheral device as recited in claim 16, wherein said speakercontroller is further configured to ramp volume back up to said poweredspeaker after restoring power to said powered speaker.
 21. A microphoneperipheral device, comprising:a microphone; a control unit configured toreceive signals on a bus coupled to said peripheral device, wherein saidcontrol unit is furtherer configured to monitor said bus and to shut offpower to said microphone after detecting bus activity below apredetermined threshold for a predetermined period of time; and saidcontrol unit further configured to monitor an audio input from saidmicrophone for activity and to restore power to said microphone inresponse to detecting a predetermined level of activity on said audioinput for a predetermined duration.
 22. The peripheral device as recitedin claim 21, wherein said control unit is further configured to powerdown said microphone in response to a command received on said bus froma computer coupled to said bus.
 23. The peripheral device as recited inclaim 21, wherein said bus comprises the Universal Serial Bus.